In cellular networks, such as networks complying to the UMTS (Universal Mobile Telecommunications System) standard, more and more traffic is due to data traffic.
Using EUL (enhanced uplink), capacity has been increased and delay is reduced. However, capacity is always short and there is a perpetual need to increase capacity.
HARQ (hybrid automatic repeat request) re-transmissions can be exploited to increase the cell and user capacity.
A higher percentage of HARQ re-transmissions can lower the air-interface load for a given user throughput. This can be achieved by setting a required percentage of BLER (block error rate) in HARQ transmission to a given target number of HARQ re-transmissions in outer-loop power control in the RNC (radio network controller).
In the prior art, outer loop power control is typically a task of the RNC, since it controls the SIR target in more than one RBS (radio base station) when a user is in soft handover. The RNC can also set a maximum SIR target for a given radio access bearer. The inner loop power control is performed at the RBS to control the power of each of its instances of user equipment. One task in the inner loop power control is to measure the SIR for each user equipment at the RBS and control the transmission power of the respective instances of user equipment to reach the SIR target received from the outer loop control.
However, the RNC is not in control of the users rate, as the granted rate is handled in the scheduler in the RBS, whereby it can be difficult to optimize the correct target number of HARQ re-transmissions required for each granted rate.
For example, a low percentage of HARQ re-transmissions might be required when aiming to have a high peak rate, since a high percentage of HARQ re-transmissions will effectively lower the peak throughput. On the other hand, a high percentage of HARQ re-transmissions might be required when on a lower granted rate, for example when there are a number of EUL users in the cell, to increase cell capacity, and as a result the per-user throughput.
Another problem is when controlling the target number of HARQ re-transmissions and target BLER from the RNC, it is not prevented that two or more users affect each others SIR (signal to interference ratio) by causing each other to raise power, potentially causing more re-transmissions and causing outer-loop power control to raise the SIR target, and thus reduce cell capacity.